In an LTE (Long-Term Evolution) radio communication system, compact femto base stations (HeNB: Home-evolved Node B) operate. In the following explanation, known base stations (eNB: evolved Node B) are referred to as “macro base stations” to distinguish them from femto base stations.
A femto base station is typically an apparatus purchased by a user and installed in a residence or business office. After installation, a femto base station is connected to a gateway device referred to as an HeNB-GW (HeNB-Gateway) that concentrates femto base stations, and is connected to a core network of the communication business by way of the HeNB-GW.
It is believed that the following problems arise under these circumstances.
(1) Frequent incidence of position registration requests to the femto base station from UE (User Equipment: terminals)
(2) Increase of load upon the core network that is beyond the HeNB-GW when the amount of UE communication increases
For the above-described problem (1), it is proposed in Patent Document 1 that the following algorithm be applied to a LTE radio communication system. In this algorithm, an FNG (Femto Network Gateway, which corresponds to HeNB-GW) converts the MNC (Mobile Network Code) that is contained in macro-position registration area ID (the identifier of a position registration area of a macro base station) to the MNC of the femtocell net and sets the macro-position registration area ID after conversion as the femto position registration area ID (the identifier of the position registration area of the femto base station). When the MNC that is contained in a position registration area ID that is reported from a base station in the vicinity is compatible with an MNC that is contained in the position registration area ID at the time of the previous position registration, position registration is not carried out by the UE, thereby enabling a decrease in the frequency of UE position registration requests. FIG. 7 of Patent Document 1 shows the sequence at the time that a UE implements position registration. In procedure 356 of this sequence, as shown in FIG. 9 of Patent Document 1, an FNG converts the femto position registration area ID of a femto base station that is included in the position registration request that is received from the UE to the macro position registration area ID of a neighboring macro base station of the femto base station and transmits the position registration request that follows this conversion to a MME (Mobility Management Entity: mobility management server) in the core network. The neighboring macro base station is a macro base station that is at a position at which the femto base station can receive the macro position registration area ID that is reported from the macro base station (the same applies to the following explanation).
However, according to 3GPP (3rd Generation Partnership Project), in an LTE radio communication system, ciphering and integrity protection can be set in data in the interest of ensuring security.
The setting of ciphering is the use of a ciphering key by the transmitting side to encode data. In this case, the receiving side decodes the data using the same ciphering key as the transmitting side.
The setting of integrity protection is performed by using of an integrity key by the transmitting side to calculate an authentication code of the data and then by adding the calculated authentication code to the data. In this case, the receiving side uses the same integrity key as the transmitting side to calculate the authentication code of the data and then verifies the integrity of the data by comparing the calculated authentication code with the authentication code that is added to the data.
However, according to TS33.401 v 9.2.0 and TS36.300 V9.2.0, which are recommendations of the 3GPP, while the setting of ciphering in NAS (Non Access Stratum) signaling is open to selection, the setting of integrity protection is required. In addition, the ciphering and integrity protection of NAS signaling is terminated at the MME. In other words, in the case of NAS signaling, decoding that employs the above-described ciphering key and verification of integrity that employs the above-described integrity key are carried out at an MME.
When the ciphering and integrity protection are set in NAS signaling, the ciphering of the position registration request by way of NAS must be cancelled in HeNB-GW in order to convert the femto position registration area ID that is contained in the position registration request that is received as the NAS signaling from a UE to a macro position registration area ID as in Patent Document 1. Still further, in the HeNB-GW, integrity protection must be reset after the above-described conversion in order that the MME does not interpret {its absence} due to the above-described conversion as the loss of integrity of the position registration request.
With regard to the above-described problem (2), a data offloading method referred to as LIPA (Local IP Access)/SIPTO (Selected IP Traffic Offload) has been proposed in Non-Patent Document 1 (S2-096108), which is a contributed article submitted to the working group “SA (Security Association) 2” of the 3GPP.
LIPA enables the offloading of data from a UE to an LAN (Local Area Network) by way of a femto base station and the transfer of data between a UE and an apparatus in the LAN. In addition, SIPTO enables the offloading of data from a femto base station directly to the Internet without being routed by way of the core network of a communication business.
In Patent Document 2, an access point (corresponding to a femto base station) is proposed that enables communication from a mobile telephone (corresponding to a UE) with, for example, a network server on the Internet by way of an IP gateway that is installed in the user's residence or office without being routed by way of the core network of a communication business in the system that is shown in FIG. 1 of Patent Document 2.
Alternatively, as shown in FIG. 1B of Patent Document 3, Patent Document 3 proposes a femto access point (corresponding to a femto base station) having means that monitors IP traffic that is transmitted and received by way of an Iu interface between a UE and a core network and determines whether to offload a packet session.
However, in the case of a configuration in which femto base stations are concentrated in an HeNB-GW, offloading from a femto base station is not necessarily required as in Non-Patent Document 1 or Patent Document 2 or 3. For example, it is possible for the HeNB-GW and not the femto base station to read the APN (Access Point Name) of a message that is transmitted to a UE from an MME in a core network or the APN of a message that is transmitted from a UE to the core network for establishing a PDN (Packet Data Network) connection and then offload traffic in accordance with the APN. This approach also enables a reduction of the load to the core network.
Still further, although there is concern in Non-Patent Document 1 (S2-096108) regarding the problem of security problems or the possibility of legal interception when implementing LIPA/SIPTO, these problems can be dealt with if the HeNB-GW is installed on the premises of a communication business. However, although the setting of ciphering in NAS signaling is currently open to selection in 3GPP, when ciphering is set, it is established that ciphering terminates at the MME. As a result, in LTE HeNB-GW, implementation of legal interception or offloading of traffic based on APN that is read from messages that are transmitted and received between an MME and UE is not recognized. For the same reason, an eNB that is a macro base station cannot offload traffic based on an APN.
In Patent Document 4, an IPsec (IP Security Protocol) tunnel is established based on IKEv2 (Internet Key Exchange version 2) between an AGW (Access Gateway: corresponding to an HeNB-GW) and a terminal (corresponding to a UE) to ensure security. Here, when security between a terminal and a base station is secured by another mechanism such as encryption of the radio link, problems arise such as an increase in the overhead for unnecessary IPsec tunnels, leading to pressure on the radio band or a decrease of processing capability of terminals. In Patent Document 4, a method is proposed in which, when security is ensured between a terminal and base station, an IPsec tunnel is provided only between the base station and an AGW, and an IPsec tunnel is not provided between the terminal and the base station. However, this method does not resolve the problems of the above-described (1) and (2).
As described hereinabove, even if femto based stations should come into wider use to cope with network traffic that will continue to increase, as long as an HeNB-GW is unable to set or cancel ciphering or integrity protection, the above-described problems will remain unsolved and concerns will remain regarding obstacles to the provision of service or to operating a communication business.
Similarly, there is concern for obstacles to the provision of services or operating a communication business even when a macro base station is unable to implement the setting or the cancelling of ciphering or integrity protection.